#include <bits/stdc++.h>
using namespace std;

int main(){
  int n, m; cin >> n >> m;
  string s, t; cin >> s >> t;
  int sa = 0; int sb = 0; int ta = 0; int tb = 0;
  for (int i = 0; i < n; i++){
    if (s[i] == 'A') sa++;
    else sb++;
  }
  for (int i = 0; i < m; i++){
    if (t[i] == 'A') ta++;
    else tb++;
  }
  cout << min(sa, ta) + min(sb, tb) << endl;
  return 0;
}